Since the dispute about an area contaminated with solvents in the old town, the keyword "contaminated sites" has attracted special attention in Oberursel.
When recently dead fish drifted on the Frankfurt side in the Urselbach, the environmental association BUND was pricked up and suspected that the construction site on the site of the former Neumühle might have something to do with it.
There, after the Second World War, displaced persons had built a glassworks on the rubble of a bronze factory.
Most recently, the three-hectare site on which the Frankfurt-based Pecan Development plans to build offices, 97 apartments and new buildings for the Ketteler-La-Roche School for Social Work was left fallow.
Correspondent for the Rhein-Main-Zeitung for the Hochtaunus district.
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However, the city has determined another reason for the contamination of the Urselbach.
A poisonous substance entered the sewage treatment plant through the sewer network and caused the biological treatment stage, in which bacteria do the cleaning process, to collapse in a short time.
Untreated sewage flowed into the stream.
"We are pretty sure that this is the cause," said Mayor Hans-Georg Brum (SPD) on Wednesday at an on-site visit.
When asked, the regional council responsible for soil and water protection confirmed this: The cause was the illegal discharge of a completely different substance that does not occur on the construction site.
"The substances in the floor did not surprise us"
Nevertheless, traces of heavy metals such as cadmium and lead can be found in the floor of the former factory. The site was already rehabilitated at the end of the nineties, and the groundwater showed no abnormalities even in the most recent investigations. But the remaining building rubble still contained debris. Therefore, prior redevelopment is part of the development of the area. For this purpose, the surface is removed down to the grown soil and filled with the supplied mother earth.
“The substances in the floor therefore did not surprise us,” said Pecan's managing director Markus Brod.
However, due to the lack of precise plans, no one knew exactly where the old cellars or masonry canals would have been.
These have now been exposed.
The BUND documented this condition with drone images and suspected that water was being illegally diverted from the construction site into the Urselbach.
However, it was a consequence of the heavy rains.
At that time, according to a spokesman for the regional council, the most heavily contaminated debris had already left.
Construction site will provide another topic of conversation
The active pumping of groundwater for about two weeks, as provided for in the rehabilitation plan, will only start in a few days, said Brod. The water level has to be lowered in order to dig the soil deeper and then refill it. "We have the permit to channel the groundwater into the Urselbach," said the managing director. Because it is harmless, you can also use the channel for it. “Samples are taken regularly.” The aim of the redevelopment concept agreed with the supervisory authority is to have the site cleared afterwards. This provides evidence that the contaminated sites have been removed.
In the meantime, it is foreseeable that the construction site will provide another topic of conversation. Because actually a ten meter wide protective strip along the stream, which is lined with trees, should remain untouched. "But there is a suspicion that the pollution extends into it," said Brod. Therefore one is in contact with the authorities. Should the strip also have to be removed, nothing will change in the stipulations in the development plan, said the head of town planning, Arnold Richter. It will then be replanted. "We want to free the entire property from encumbrances."